This invention relates to a clamp for two picture frame members that are being glued together along a miter joint. The clamp is designed to exert a relatively high pressure on the frame members and surfaces that form the miter joint, to reduce the gluing time and provide a relatively strong glue joint. Optimally, the miter joint can be created solely by gluing, without the necessity for mechanical fasteners. The clamp is designed to be a relatively low cost, rugged tool that can be manually operated to achieve a fast cycle time between the unclamped condition and the clamped condition.
In the past, clamps have been used for assembling picture frames. U.S. Pat. No. 4,019,270 issued to Leonard D. Trowbridge, shows a clamp assembly that includes four comer clamp elements attached to four diagonal straps. An actuator screw is used to draw the straps toward the picture frame axis, whereby the corner clamp elements exert pressure on the outer edges of the picture frame members.
U.S. Pat. No. 5,730,433 issued to John Veres, shows a picture frame clamp that includes a slider 6 having prongs 15 engageable with the inner edges of the two picture frame members that are positioned against two stationary stops 4,4. As the prongs engage the inner edges of the picture frame members, the prongs are intended to deflect slightly toward the slider 6 axis, thereby sliding the picture frame members along stops 4,4. The intent is to achieve a relatively high pressure at the miter joint. There is some doubt that prongs 15 can produce the desired effect on a consistent basis.
The present invention concerns a picture frame clamp, wherein a stationary stop engages the inner edges of two picture frame members; and a movable clamp member is advanced toward the stationary stop to exert clamping pressures on the outer edges of the picture frame members. The movable clamp member has a concave V-shaped clamp surface, such that the clamp member generates opposing inwardly directed pressures against the picture frame members. As a result, the mating end surfaces of the frame members are forced tightly together to achieve intimate contact between the miter joint surfaces and the glue. Excess glue is squeezed out of the miter joint, so that curing time is somewhat shortened. In experimental situations, miter joint pressures on the order of one thousand p.s.i. have been achieved, using an apparatus of the present invention. Strong miter glue joints have been consistently obtained, using only glue as the connecting medium (i.e. without nails, brads or other mechanical fasteners).
Further features of the invention will be apparent from the attached drawings and description of an illustrative embodiment of the invention.